2. Must have a willing unrelated adult donor (bone marrow or peripheral blood). Donors may have a single mismatch (i.e. be a 7/8) and this mismatch may be at the allele or antigen level; however, donors with allele level disparity should be given preference over those with antigen level disparity. The use of mismatched donors in which disparity is only in the host versus graft direction (because of recipient homozygosity) is discouraged because of the potentially heightened risk for graft rejection. Centers may perform extended typing (e.g. DQB1 and DPB1) according to institutional practices and use these results in selecting donors; however, it is recommended that this extending typing be used only to select between donors who are equally well matched with the recipient at the A, B, C and DRB1.